Agricultural air seeders include generally an implement frame and a plurality of furrow openers spaced across a width of the frame, and movable to a lowered operating position where the furrow openers engage the ground to create furrows as the frame moves along a field. Agricultural products such as seed, fertilizer, and the like are carried in tanks mounted on the frame or a cart pulled with the frame and distributed to the furrow openers by a product distribution system where one or more fans create one or more air streams and metering devices dispense the agricultural products into the air streams and the products are carried through an air distribution network made up of conduits and manifolds to the furrow openers, and then into the furrows. Furrow opener assemblies often create two (or more) separate furrows, such as one furrow for seed and a separate furrow for fertilizer, and separate air streams carrying different agricultural products are connected so as to deposit the different products in the separate furrows. In other air seeders, separate furrow opener assemblies may be used to create the separate furrows.
There are different types of product distribution systems used on present day air seeders. In a Class A product distribution system, all agricultural products destined for a given set of furrows spaced across the width of the implement are metered into a single air stream in a primary supply conduit connected to a primary manifold. Such manifolds are generally a thin cylinder with an inlet in a top or bottom of the cylinder connected to the supply conduit to receive the air stream carrying agricultural products, and a number of outlet ports equally spaced around a circumferential wall. Flat fan manifolds are also known where the supply conduit directs the product air stream into one end of the flat manifold body which divides the product air stream into channels with ports at the ends of the channels on the opposite end of the manifold body. Delivery conduits are connected to each port to carry the air stream further downstream to another manifold or to a furrow opener as the case may be.
In such a Class A product distribution system the primary manifold provides primary division of the air stream and the agricultural products carried therein by dividing and directing the air stream into a number of different delivery conduits, each of which is in turn connected to a secondary manifold. The secondary manifold provides secondary division of the air stream and the agricultural products carried therein by dividing and directing the air stream into a number of different secondary conduits, each of which is connected to a furrow opener to direct the air stream, and the agricultural products carried therein, into a selected furrow.
In a Class B product distribution system the metering device itself is divided into a number of sections such that primary division of the agricultural products takes place prior to the products entering the air stream. Each conduit from a meter section is connected to a manifold which provides secondary division of the air stream and the agricultural products into a number of different secondary conduits, each of which is connected to a furrow opener as in the Class A system.
Present day air seeders are often 80 or more feet wide, and a problem arises when a strip of a field to be seeded is much narrower than the seeder, as a considerable width of the field will be overlapped and seeded twice. It is most undesirable to leave even a narrow strip of a field unseeded as, without crop competition, weeds will flourish in the strip providing seed for future years weed growth. Seeding the adjacent field area twice, however, wastes valuable seed and fertilizer, and the crop on the twice seeded field area generally has reduced yield and/or quality.
Thus it is desirable to provide a means to stop the delivery of agricultural products to furrow openers in the overlap area by providing individual control of the delivery of agricultural products to a number of different sections of furrow openers across the width of the air seeder. U.S. Pat. No. 7,690,440 to Dean et al. discloses a Class B product distribution system where the metering device is divided into a number of sections, and where gates are provided at each meter section that may be opened or closed to start or stop product flow from each meter section. The air seeder is configured so that each meter section supplies agricultural products to a downstream manifold and from there to furrow openers that are laterally arranged in order across a section of the width of the seeder so that stopping product flow to any manifold stops product flow to a section of the air seeder. Thus as the strip of field to be seeded narrows to less than the width of the air seeder, product delivery is stopped to sections of the air seeder passing over previously seeded ground.
U.S. Pat. No. 7,555,990 to Beaujot takes a different approach by providing valves on the outlet ports of the manifold. The described system has a single manifold downstream from the metering device, and valves are provided on each port of the manifold. Each port can thus be opened or closed, such that the delivery of the air stream with the entrained agricultural products to each furrow opener can be stopped or started, however a problem arises when a port is closed and the flow of air through the downstream delivery conduit connected to the furrow opener is shut off. These delivery conduits very often do not slope down all the way from the manifold to the furrow opener, but have low areas where the conduit dips down and then rises. When the manifold ports are blocked, the air is instantly cut off and agricultural products in the downstream conduit are no longer carried along by the air stream but simply fall down, and can thus gather into one of these low areas and block the conduit such that when the port gate is opened again the air stream will not flow through the blocked conduit and the furrow opener will receive no product.
This problem of blocked conduits downstream from a blocked port is addressed by U.S. Pat. No. 8,635,963 to Friggstad by having a two-way valve at each port which can block product flow through the port and simultaneously expose the blocked port to a purging air flow that blows product in the downstream conduit out into the furrow. A plenum of pressurized air is fluidly coupled to the two-way valve to provide the purging air flow to any exit port of the manifold that has been shut off from product flow.
When some of the manifold ports are closed in the systems of Beaujot and Friggstad, the flow of air through the downstream delivery conduits connected to the furrow openers is shut off and the air stream entering the manifold then must flow out through the open ports such that an increased amount of air flows out each of the open ports. As the number of closed ports increases, more and more air tries to flow through the open ports and back pressure in the manifold increases. With the fans most commonly used in air seeders to generate the air streams used for distributing agricultural products through conduits, as the back pressure in the conduits increases, the volume of air moved decreases, and the velocity of the moving air decreases.
Thus, in the system of Beaujot, as back pressure in the manifold increases, the volume of the air stream entering the manifold is reduced, and the velocity of the air flowing through the supply conduit feeding the manifold is reduced. The air stream must move through the supply conduit at a minimum velocity that is sufficient to keep the agricultural products entrained in the air stream suspended therein. This critical velocity will be higher in a vertical section of the supply conduit than in a horizontal section, as the air stream must move the agricultural products upward against the force of gravity as opposed to moving the product laterally.
If the velocity drops below this “critical” velocity, the particles of agricultural product will drop out of the air stream. Thus, in the Beaujot and Friggstad systems, as ports are closed the velocity of the air stream will at some point fall below the critical velocity, the agricultural products will start to drop out of the air stream, and lay in the bottom of the supply conduit.
U.S. Pat. No. 8,690,488 to Jagow et al. addresses this problem. In Jagow when the port valve is closed to block product flow, an exhaust valve on the supply conduit is opened to exhaust a flow of air similar to that blocked when the port valve is closed. The Jagow system thereby keeps substantially the same amount of air flowing through the supply conduit which addresses the air flow problems present with the Beaujot and Friggstad systems. In one version the exhaust air is directed through a two-way valve which either opens the port to allow product flow into the downstream conduit while blocking the exhaust air flow, or blocks the port to stop product flow while opening the exhaust and directing the exhaust air into the downstream conduit to purge the downstream conduit of product, similar to the system of Friggstad.